Erythrocytes in the blood are responsible for oxygen transport throughout the body and play an important role in maintaining oxygen levels constant in vivo. If, on account of bleeding due to certain kinds of disease, as well as to accidents or surgical operations, the erythrocyte counts or hemoglobins level in the blood decrease, a sense of fatigue, dizziness, shortness of breath and other anemic symptoms will develop. In anemia, the entire body will be exposed to oxygen deficiency and under such hypoxic conditions, the living body performs a compensatory reaction, in which the hematopoietic factor erythropoietin (hereinafter also referred to as EPO) which promotes the formation of erythrocytes is produced primarily from the kidney to increase the erythrocyte and hemoglobin levels in the blood, thus helping to ameliorate anemia. However, in certain kinds of disease, this erythropoietic action of erythropoietin is impaired and chronic anemia persists. For example, in patients with renal failure who have disorder in the kidney, it is known that the above-described mechanism for erythropoietin production under hypoxic conditions fails to work properly, causing them to present with a type of anemia (renal anemia) which is characterized by reduced erythrocyte counts and hemoglobin levels (see Non-Patent Documents 1 and 2).
The treatment of renal anemia and the anemia that accompanies cancer chemotherapy or medication of patients with HIV infection is currently carried out by erythropoiesis stimulating agents (ESA) such as genetically recombinant human erythropoietin preparations. The ESA greatly contributes to improving a patient's quality of life by increasing the erythrocyte counts and hemoglobin levels sufficiently to ameliorate the symptoms that accompany anemia. On the other hand, however, the currently available ESAs are all biologics in the form of expensive injections, so it is desired to develop an orally administrable pharmaceutical drug for the treatment of anemia.
A recent study has reported that erythropoietin also has an action for protecting tissues such as hearts and brains placed under the hypoxic conditions that accompany anemia. Therefore, orally administrable ESA preparations have the potential to find a wide range of applications covering not only renal and other types of anemia that result from various causes but also a diversity of ischemic diseases (see Non-Patent Document 3).
A substance that may be mentioned as a factor that increases the production of erythropoietin is a hypoxia-inducible factor (hereinafter also referred to as HIF). The HIF is a transcription factor including an α-subunit the degradation of which is regulated by changes in oxygen density and a β-subunit that is expressed constantly. Prolyl hydroxylases (PHD-1, -2 and -3) are known as factors that regulate the degradation of HIF's α-subunit (HIF-α). Under normal oxygen pressure conditions, the proline residues of HIF-α are hydroxylated by these prolyl hydroxylases and the HIF-α is rapidly degraded by proteasome. Under hypoxic conditions, on the other hand, the activity of prolyl hydroxylases is lowered, so the degradation of HIF-α is suppressed, thus promoting the transcription of the erythropoietin- and other HIF-responsive genes. Consequently, by inhibiting the prolyl hydroxylases, the stabilization of HIF-α is promoted, making it possible to increase the production of erythropoietin (see Non-Patent Documents 1, 2 and 4).
The compounds of the present invention provide means for inhibiting the activities of those prolyl hydroxylases to increase the amount of erythropoietin, thereby treating anemia. As another benefit, not only anemia but also various other ischemic diseases (e.g. brain stroke, myocardial infarction, and ischemic renal disorder) and diabetic complications (nephropathy, retinopathy, and neuropathy) can also be treated or prevented or improved or mitigated in symptoms by administering the compounds of the present invention (see Non-Patent Document 5).
Common PHD inhibitors reported to date include 4-hydroxyisoquinoline derivatives (see Patent Document 1), 5-hydroxy-3-oxo-2,3-dihydro-1H-pyrazole derivatives (see Patent Document 2), 4-hydroxy-2-oxo-1,2-dihydroquinoline derivatives (see Patent Document 3), 3-hydroxypyridine derivatives (see Patent Document 4), 2-oxo-2,3-dihydroindole derivatives (see Patent Document 5), etc. but compounds having the structures according to the present invention have not been disclosed. Also reported to date include are 6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydropyrimidine derivatives (see Patent Document 6), 4-hydroxy-6-oxo-1,6-dihydropyrimidine derivatives (see Patent Document 7), 5-hydroxy-3-oxo-2,3-dihydropyridazine derivatives (see Patent Document 8), 6-hydroxy-4-oxo-4H-1,3-dioxin derivatives (see Patent Document 9), 4-hydroxy-2-oxo-1,2,5,7-tetrahydrofluoro[3,4-b]pyridine derivatives (see Patent Document 10), 4-hydroxy-2-oxo-1,2-dihydropyridine derivatives (see Patent Documents 11 and 12), etc. but compounds having the structures according to the present invention have not been disclosed.